By Marc Lipsitch How many people in a population will need to get a COVID-19 vaccine before herd immunity is achieved? This question has been all over the news lately, with speculations of 70%, 80%, or other numbers. The math needed to answer this question is simple, but the question is, in my opinion, unanswerable at this point because the inputs to the math — the numbers to plug into … Continue reading COVID-19 Vaccines and Herd Immunity